Hanger assemblies are used to insert and support strings of tubing within downhole wellbores and are typically structurally incorporated with the wellhead. Therefore, before an additional string of tubing can be inserted into an existing wellbore, the wellhead must first be modified to include an additional bowl for receiving the new hanger assembly. This often also requires changing out the valves and possibly the entire wellhead, and is thus expensive and time consuming.
An additional problem results when a subsurface safety device has been inserted into the wellbore to prevent uncontrolled flow. Hanging an additional string of tubing through such a safety device renders it unoperable, and would place offshore wells in noncompliance with government safety regulations.
One particular instance in which the above problems are experienced is when hanging a siphon string to extend the flowing productive life of a well. A siphon string is a reduced diameter string of tubing used to effectively reduce the diameter of the production tubing. When installed in the wellbore, the velocity of the oil and gas travelling up the tubing is increased due to the reduced flow area, thereby enabling additional oil and gas to be produced under the well's natural pressure prior to the expense of installing artificial lift systems.
However, the cost of working over the well and/or modifying the wellhead to install the siphon string hanger assembly is relatively high when compared to the expected amount of additional recovery. In addition, siphon strings presently cannot be used in offshore wells due to their interference with the required subsurface safety devices.
Therefore, there is a need for an inexpensive and simple device for hanging tubing below the wellhead within the casing or production tubing which does not require modification of the wellhead and does not interfere with the operation of subsurface safety devices.